1. Field of the Invention
The present invention relates to a slurry for CMP (Chemical Mechanical Polishing) of copper and to a method of manufacturing a semiconductor device by making use of the slurry. In particular, the present invention relates to formation of a damascene wiring of copper, which is designed to be employed in a DRAM or a high-speed logic LSI.
2. Description of the Related Art
In recent years, attention has been drawn to the employment of copper as a wiring material for LSI. Since the working of a Cu layer by means of RIE (Reactive Ion Etching) is accompanied with difficulties, the working of a Cu layer has been generally performed by making use of a damascene wiring-forming method where the CMP method (Chemical Mechanical Polishing Method) is employed.
The working by means of chemical CMP is performed as follows. Namely, a protective film made of an oxide or an organic compound (an organic Cu complex) is formed by chemical reaction on the surface of a Cu layer, and then, the Cu layer is polished while the surface of the Cu layer is protected by this protective film. Therefore, the performance of the working by means of CMP is greatly influenced by the characteristics of the protective film to be employed. Namely, a protective film made of an organic Cu complex which is excellent in flexibility is more preferable than a protective film made of a Cu oxide or an inorganic material in that the polishing rate of Cu layer is relatively high and the erosion of Cu layer can be minimized. Incidentally, if it is desired to form the protective film on the surface of a Cu layer by making use of an organic Cu complex, it can be realized by incorporating a complexing agent which is capable of forming the organic Cu complex into a polishing slurry.
However, the method of forming the protective film made of the organic Cu complex is accompanied with the problem that the resultant protective film is hydrophobic because of the fact that the protective film is formed of an organic material. If the protective film is hydrophobic, it will give rise to instability of the performance of CMP. For example, since residual abrasion dust (residual dust created from the polishing) of the organic Cu complex is hydrophobic, it is not dissolved in a polishing slurry, so that residual abrasion dust is caused to accumulate in a polishing pad. If this residual abrasion dust is accumulated in the polishing pad, the polishing rate of a Cu layer is considerably decreased.
Further, since the surface of a Cu layer being polished is also hydrophobic, residual abrasion dust is caused to adhere onto the surface of the Cu layer. Further, since the Cu layer is polished in the presence of residual abrasion dust, scratches are caused on the surface of the Cu layer.
Therefore, it is required that the protective film made of an organic Cu complex is made hydrophilic. It is conceivable to incorporate a surfactant into the complexing agent in order to hydrophilize the protective film formed of an organic Cu complex. However, if the surfactant is formed of an ionic surfactant, the surfactant may react with Cu to form a compound or be adsorbed onto the particles in the polishing slurry, thereby deteriorating the performance of CMP. On the other hand, if the surfactant is formed of a nonionic surfactant, the surfactant may be prevented from forming a complex with Cu, thus allowing the surfactant to adsorb onto a hydrophobic organic complex that may be formed through the reaction between Cu and the complexing agent, thereby improving, to some extent, the hydrophilicity of the protective film. However, since the magnitude of hydrophilization of the protective film is insufficient in this case, the effect obtained from this hydrophilization of the protective film would be negligible.